Preparation method and application of defect-rich dual-ligand metal-organic framework ultrathin nanosheets

Abstract

The present invention discloses a preparation method and application of defect-rich dual-ligand metal organic framework ultrathin nanosheets, belonging to the technical field of electrocatalytic oxygen evolution and water decomposition hydrogen production. The present invention grows defect-rich dual-ligand metal organic framework ultrathin nanosheets on a carrier through a one-step solvothermal method. The competitive coordination of the dual ligands effectively regulates the electron spin state of the Ni site and optimizes the e g orbital electron occupancy, thus achieving faster deprotonation of Ni-OH*. In alkaline media, Ni-TDC x BDC 1‑x The material exhibited excellent OER performance and good electrical conductivity, and had long-term stability. It also showed excellent catalytic performance and stability in the overall hydrolysis reaction, indicating that the Ni-TDC prepared by the present invention x BDC 1‑x The material can be regarded as a highly efficient electrocatalytic oxygen evolution reaction catalyst with significant application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic oxygen evolution and water decomposition to produce hydrogen, and in particular relates to a preparation method and application of a defect-rich dual-ligand metal organic framework ultrathin nanosheet. Background Art

[0002] In recent decades, the global demand for energy has continued to grow, prompting the search for ideal energy carriers to store renewable energy sources, such as wind and solar energy. Electrochemical water splitting is considered a sustainable method for the large-scale production of hydrogen as a clean fuel. However, a key step in the oxidation half-reaction, the oxygen evolution reaction (OER), suffers from sluggish kinetics and high overpotential due to a multi-step proton coupling process, becoming a bottleneck restricting the efficiency of hydrogen production. The kinetics of the OER are determined by the rate distribution (RDS), i.e., the adsorption / desorption of intermediates on active sites. To achieve fast reaction kinetics in the OER process, the hybridization strength between the transition metal 3d orbitals and the oxygen intermediate 2p orbitals must be optimized. Therefore, the study of the spin configuration of transition metals is crucial for the development of efficient and durable OER catalysts. Therefore, the selection of two-dimensional metal-organic frameworks (2D MOFs) with well-defined active sites, uniform morphology, and excellent electron transfer as model catalysts has certain advantages.

[0003] In the basic transition metal OER mechanism, all intermediates interact with the metal surface through oxygen atoms. Among them, the bonding interaction with oxygen-containing intermediates (MO, M is the catalytically active metal center) is crucial to the overall OER activity. Therefore, the MO bond strength is considered to be an "activity descriptor" of OER catalytic activity. In addition, according to molecular orbital theory, OER activity is closely related to the e of the transition metal cation. g The occupation level is closely related, because e g The electrons in the orbital can effectively interact with oxygen-containing adsorbents. Excellent OER catalysts should have an electron occupancy close to 1 to promote electron transfer between surface active sites and adsorbed intermediates. Therefore, it is very important to develop effective strategies to change the electron spin (or optimize the electron occupancy) and regulate the interaction between oxygen-containing intermediates and active sites. In addition, improving the electrochemical performance of nickel-based electrode materials by adjusting the exposed electrochemical reaction active sites at the atomic scale remains a considerable challenge.

[0004] Therefore, there is an urgent need for an electrode material that uses a two-dimensional metal-organic framework as a model catalyst and can adjust the exposed electrochemical reaction active sites at the atomic scale to solve the above problems. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a preparation method and application of defect-rich dual-ligand metal-organic framework ultrathin nanosheets.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is a method for preparing ultrathin nanosheets of defect-rich dual-ligand metal organic frameworks, which is to grow a metal organic framework formed by metal and dual ligands on a carrier by a one-step solvothermal method to obtain the ultrathin nanosheets of defect-rich dual-ligand metal organic frameworks (referred to as Ni-TDC). x BDC 1-x );

[0008] The dual ligands are 1,4-terephthalic acid (H2BDC) and 2,5-thiophenedicarboxylic acid (H2TDC).

[0009] This invention utilizes a dual-ligand competitive coordination strategy involving 1,4-terephthalic acid and 2,5-thiophenedicarboxylic acid to synthesize ultrathin metal-organic framework (MOF) nanosheets on a support via a one-step solvothermal method. Competitive coordination of the ligands introduces lattice strain into the synthesized MOF. This intense micromechanical strain distorts the atomic arrangement, exposing more metal active sites. The resulting dual-ligand MOF ultrathin nanosheets exhibit excellent electrocatalytic performance in the alkaline oxygen evolution reaction (OER) and outstanding overall water splitting performance.

[0010] The two organic ligand sources play the following roles in the reaction process: (1) They participate in the construction of the Ni-MOF structure by competing with nickel ions to form coordination bonds; (2) Since Ni-TDC and Ni-BDC have very similar or multiple lattice constants, it means that subtle lattice strain can be introduced into their structure without destroying the regular structure of MOF; (3) Since H2BDC molecules are longer than H2TDC, the incorporation of H2BDC into Ni-TDC may cause the MOF lattice to expand, thereby generating a large number of unsaturated Ni sites and changing the coordination environment of Ni atoms, which in turn leads to the growth of Ni-O bonds.

[0011] Furthermore, the method for growing a metal-organic framework formed by a metal and a dual ligand on a carrier by a one-step solvothermal method includes the following steps: dissolving a nickel source, 1,4-terephthalic acid and 2,5-thiophenedicarboxylic acid in an organic solvent to obtain a reaction solution; placing the carrier in the reaction solution to perform a solvothermal reaction to obtain the defect-rich dual ligand metal-organic framework ultrathin nanosheets.

[0012] Furthermore, the nickel source is nickel nitrate hexahydrate; the organic solvent is N,N-dimethylformamide (DMF) aqueous solution; and the carrier is carbon fiber paper.

[0013] Carbon fiber paper has good porosity and conductivity, and is resistant to high temperatures and corrosion. Its skeleton will not be destroyed under extreme conditions, making it suitable as a carrier for dual-ligand metal-organic framework ultra-thin nanosheets.

[0014] The organic solvent N,N-dimethylformamide aqueous solution plays the following roles: (1) It stabilizes the structure of Ni-MOF by coordinating with nickel ions to form coordination bonds; (2) DMF acts as a reaction regulator during the synthesis process, adjusting the polarity of the reaction solvent, controlling the formation of Ni-MOF, and improving its purity; (3) It forms connections with metal Ni ions during the synthesis process, participates in the construction of the porous structure of Ni-MOF, and regulates the size and shape of the pores.

[0015] In addition, the present invention selects DMF aqueous solution as the solvent instead of other organic solvents because DMF aqueous solution has the following advantages: (1) Solubility: DMF aqueous solution can dissolve most organic substances and many inorganic substances, which makes it particularly useful in synthesis, especially in reactions that require high solubility. (2) Strong polarity: DMF is a polar aprotic solvent, which means that it has a high dielectric constant and can stabilize the charge, thereby promoting the progress of ionic reactions. (3) Deprotonation: At high temperatures, DMF can decompose to produce a small amount of dimethylamine, which helps deprotonate the ligand, thereby promoting the coordination process between the metal and the ligand.

[0016] Furthermore, the ratio of the sum of the amount of nickel atoms in the nickel source and the amount of the biligand is 1:1; in terms of molar ratio, the nickel atoms in the nickel source: 1,4-terephthalic acid = 1: (0.2-0.8); and the amount ratio of the nickel source to the organic solvent is 0.5 mmol: 6 mL.

[0017] Furthermore, the ratio of the nickel source to the carrier is 0.5 mmol: 2 cm 2 (carrier surface area).

[0018] Furthermore, the volume ratio of N,N-dimethylformamide to water in the N,N-dimethylformamide aqueous solution is 4:2.

[0019] Furthermore, the temperature of the solvent thermal reaction is 120° C., and the time of the solvent thermal reaction is 12 h.

[0020] Furthermore, after the solvothermal reaction is completed, washing and drying operations are also included, specifically: the carbon fiber paper loaded with defect-rich dual ligand metal organic framework ultrathin nanosheets after the solvothermal reaction is rinsed with ethanol three times, and then vacuum dried at 60°C for 12 hours.

[0021] The method further includes pre-treating the carrier, specifically by cutting the carbon fiber paper into 1 cm x 2 cm pieces, performing a hydrothermal reaction in a dilute nitric acid solution, and then washing with deionized water and ethanol. By subjecting the carbon fiber paper to a hydrothermal reaction in a dilute nitric acid solution, the present invention activates the carbon fiber paper surface and enhances its adsorption efficiency for the dual-ligand metal-organic framework ultrathin nanosheets.

[0022] Furthermore, the mass concentration of the dilute nitric acid solution is 99.9%.

[0023] Furthermore, the temperature of the hydrothermal reaction is 100° C., and the time of the hydrothermal reaction is 4 hours.

[0024] Furthermore, the specific operation of the washing is: ultrasonically washing the product after the hydrothermal reaction in deionized water and ethanol for 15 minutes respectively, and drying it naturally after the pH reaches 7.

[0025] The present invention prepares defect-rich dual-ligand metal-organic framework ultrathin nanosheets via a one-step solvothermal method. The preparation method has the following advantages: (1) Simplified synthesis process: The one-step solvothermal method is simple to operate and avoids the multi-step reaction that reduces yield. (2) Simple raw materials: Only two organic ligands, a metal nickel source, and an organic solvent are required, making the synthesis easy and the raw materials readily available. (3) Improved product purity: Solvothermal growth on carbon fiber paper can reduce the generation of impurities.

[0026] The second technical solution of the present invention: a defect-rich dual-ligand metal-organic framework ultrathin nanosheet prepared by the above-mentioned preparation method of the defect-rich dual-ligand metal-organic framework ultrathin nanosheet.

[0027] The third technical solution of the present invention: an application of the above-mentioned defect-rich biligand metal organic framework ultrathin nanosheet in the electrocatalytic oxygen evolution reaction.

[0028] Furthermore, the defect-rich biligand metal organic framework ultrathin nanosheet is used as a catalyst for electrocatalytic oxygen evolution reaction.

[0029] Furthermore, the defect-rich dual-ligand metal organic framework ultrathin nanosheet is used as an anode for oxygen evolution reaction in a full water splitting system.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] (1) The present invention grows defect-rich biligand metal organic framework ultrathin nanosheets on a carrier by a simple one-step solvent thermal method to obtain defect-rich biligand metal organic framework ultrathin nanosheets (Ni-TDC x BDC 1-x ), the competitive coordination of the dual ligands effectively regulates the electronic spin state of the Ni site and optimizes the eg orbital electron occupancy, thus achieving faster deprotonation of Ni-OH*. In alkaline media, the new Ni-TDC x BDC 1-x The material exhibits excellent OER performance and good electrical conductivity, and has long-term stability. It also exhibits excellent catalytic performance and stability in the overall hydrolysis reaction, indicating that the Ni-TDC prepared by the present invention x BDC 1-x The material can be regarded as a highly efficient electrocatalytic oxygen evolution reaction catalyst with significant application prospects.

[0032] (2) The preparation method provided by the present invention has the advantages of simplified process, easy access to raw materials and significantly shortened preparation time, and has commercial potential. More importantly, the prepared Ni-TDC x BDC 1-x The material can be directly used in the full water splitting system as an anode material, thereby greatly improving its practicality and convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0034] Figure 1 Ni-TDC prepared in Example 1-3 x BDC 1-x and X-ray powder diffraction patterns of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0035] Figure 2 Ni-TDC prepared in Example 1-5 x BDC 1-x And the Raman spectra of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0036] Figure 3 Ni-TDC prepared in Example 1-3 x BDC 1-x and scanning electron micrographs of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0037] Figure 4 Ni-TDC prepared in Example 1 0.6 BDC 0.4 Various electron microscope images;

[0038] Figure 5 Ni-TDC prepared in Example 1 0.6 BDC0.4 And the thermogravimetric curves of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0039] Figure 6 Ni-TDC prepared in Example 1 0.6 BDC 0.4 And the nitrogen isothermal adsorption-desorption curves of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0040] Figure 7 Ni-TDC prepared in Example 1 0.6 BDC 0.4 and X-ray photoelectron spectra of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0041] Figure 8 Ni-TDC prepared in Example 1 0.6 BDC 0.4 As well as the electron paramagnetic resonance curves and near-edge absorption spectra of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0042] Figure 9 Ni-TDC prepared in Example 1 0.6 BDC 0.4 A series of in situ Raman spectra;

[0043] Figure 10 Ni-TDC prepared in Example 1 0.6 BDC 0.4 And the density functional theory calculation diagrams of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2;

[0044] Figure 11 Ni-TDC prepared in Example 1-3 x BDC 1-x And the electrochemical performance test results of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2 in 1.0 M KOH;

[0045] Figure 12 This is the process and results of total water decomposition. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0049] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0050] Example 1

[0051] A method for preparing defect-rich dual-ligand metal-organic framework ultrathin nanosheets, the specific steps are as follows:

[0052] (1) Cut the carbon fiber paper into 1×2cm 2 The size was then hydrothermally reacted in a 99.9% nitric acid solution at 100°C for 4 hours. The product was then ultrasonically washed in deionized water and ethanol for 15 minutes each until the pH reached 7, and then naturally dried for later use.

[0053] (2) 0.5 mmol of nickel nitrate hexahydrate, 0.3 mmol of thiophene-2,5-dicarboxylic acid, and 0.2 mmol of 1,4-terephthalic acid were added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide were mixed in a volume ratio of 2:4), and ultrasonically treated for 1 h to obtain a reaction solution.

[0054] (3) The carbon fiber paper treated in step (1) was placed in the reaction solution prepared in step (2), and the reaction was carried out in an oven at 120°C for 12 hours. After the reaction was completed, the carbon fiber paper was naturally cooled, and then washed with ethanol three times, and then vacuum dried at 60°C for 12 hours to obtain Ni-TDC. 0.6 BDC 0.4 .

[0055] Example 2

[0056] A method for preparing defect-rich dual-ligand metal-organic framework ultrathin nanosheets, the specific steps are as follows:

[0057] (1) Cut the carbon fiber paper into 1×2cm 2 The size was then hydrothermally reacted in a 99.9% nitric acid solution at 100°C for 4 hours. The product was then ultrasonically washed in deionized water and ethanol for 15 minutes each until the pH reached 7, and then naturally dried for later use.

[0058] (2) 0.5 mmol of nickel nitrate hexahydrate, 0.4 mmol of thiophene-2,5-dicarboxylic acid, and 0.1 mmol of 1,4-terephthalic acid were added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide were mixed in a volume ratio of 2:4), and ultrasonically treated for 1 h to obtain a reaction solution.

[0059] (3) The carbon fiber paper treated in step (1) was placed in the reaction solution prepared in step (2), and the reaction was carried out in an oven at 120°C for 12 hours. After the reaction was completed, the carbon fiber paper was naturally cooled, rinsed with ethanol three times, and then vacuum dried at 60°C for 12 hours to obtain Ni-TDC. 0.8 BDC 0.2 .

[0060] Example 3

[0061] A method for preparing defect-rich dual-ligand metal-organic framework ultrathin nanosheets, the specific steps are as follows:

[0062] (1) Cut the carbon fiber paper into 1×2cm 2 The size was then hydrothermally reacted in a 99.9% nitric acid solution at 100°C for 4 hours. The product was then ultrasonically washed in deionized water and ethanol for 15 minutes each until the pH reached 7, and then naturally dried for later use.

[0063] (2) 0.5 mmol of nickel nitrate hexahydrate, 0.1 mmol of thiophene-2,5-dicarboxylic acid, and 0.4 mmol of 1,4-terephthalic acid were added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide were mixed in a volume ratio of 2:4), and ultrasonically treated for 1 h to obtain a reaction solution.

[0064] (3) The carbon fiber paper treated in step (1) was placed in the reaction solution prepared in step (2), and the reaction was carried out in an oven at 120°C for 12 hours. After the reaction was completed, the carbon fiber paper was naturally cooled, rinsed with ethanol three times, and then vacuum dried at 60°C for 12 hours to obtain Ni-TDC. 0.2 BDC 0.8 .

[0065] Example 4

[0066] The difference from Example 1 is that in step (2), 0.5 mmol of nickel nitrate hexahydrate, 0.25 mmol of thiophene-2,5-dicarboxylic acid and 0.25 mmol of 1,4-terephthalic acid are added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide are mixed in a volume ratio of 2:4) to obtain Ni-TDC. 0.5BDC 0.5 .

[0067] Example 5

[0068] The difference from Example 1 is that in step (2), 0.5 mmol of nickel nitrate hexahydrate, 0.2 mmol of thiophene-2,5-dicarboxylic acid and 0.3 mmol of 1,4-terephthalic acid are added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide are mixed in a volume ratio of 2:4) to obtain Ni-TDC. 0.4 BDC 0.6 .

[0069] Comparative Example 1

[0070] A method for preparing a Ni-TDC material, comprising the following steps:

[0071] (1) Cut the carbon fiber paper into 1×2cm 2 The size was then hydrothermally reacted in a 99.9% nitric acid solution at 100°C for 4 hours. The product was then ultrasonically washed in deionized water and ethanol for 15 minutes each until the pH reached 7, and then naturally dried for later use.

[0072] (2) 0.5 mmol of nickel nitrate hexahydrate and 0.5 mmol of thiophene-2,5-dicarboxylic acid were added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide were mixed in a volume ratio of 2:4), and ultrasonically treated for 1 h to obtain a reaction solution.

[0073] (3) The carbon fiber paper treated in step (1) was placed in the reaction solution prepared in step (2), and the mixture was kept in an oven at 120° C. for 12 h. After the reaction was completed, the mixture was naturally cooled, and the carbon fiber paper was rinsed three times with ethanol, and then vacuum-dried at 60° C. for 12 h to obtain Ni-TDC.

[0074] Comparative Example 2

[0075] A method for preparing Ni-BDC material, the specific steps are as follows:

[0076] (1) Cut the carbon fiber paper into 1×2cm 2 The size was then hydrothermally reacted in a 99.9% nitric acid solution at 100°C for 4 hours. The product was then ultrasonically washed in deionized water and ethanol for 15 minutes each until the pH reached 7, and then naturally dried for later use.

[0077] (2) 0.5 mmol of nickel nitrate hexahydrate and 0.5 mmol of 1,4-terephthalic acid were added to 6 mL of a mixed solution of N,N-dimethylformamide and water (water and N,N-dimethylformamide were mixed in a volume ratio of 2:4), and ultrasonically treated for 1 h to obtain a reaction solution.

[0078] (3) placing the carbon fiber paper treated in step (1) into the reaction solution prepared in step (2), and carrying out the reaction in an oven at 120° C. for 12 h. After the reaction is completed, the carbon fiber paper is naturally cooled, rinsed with ethanol three times, and then vacuum dried at 60° C. for 12 h to obtain Ni-BDC.

[0079] Comparative Example 3

[0080] Preparation of Pt / C electrode materials

[0081] 2 mg of Pt / C (commercially available) was weighed and added to a mixed solution of 50 μL deionized water, 50 μL anhydrous ethanol, and 25 μL Nafion solution. The mixture was dissolved by ultrasonication for 30 min, and then the ultrasonically homogenized Pt / C slurry was dropped on a 0.5 cm 2 Place on carbon fiber paper and dry at room temperature.

[0082] Comparative Example 4

[0083] Preparation of RuO2 electrode materials

[0084] 2 mg of RuO2 (commercially available) was weighed and added to a mixed solution of 50 μL deionized water, 50 μL anhydrous ethanol and 25 μL Nafion solution. The mixture was dissolved by ultrasonication for 30 min. The RuO2 slurry homogenized by ultrasonication was then dropped on a 0.5 cm 2 Place on carbon fiber paper and dry at room temperature.

[0085] Effect verification

[0086] 1. Phase structure, morphology characterization, electron spin state characterization and density functional theory calculation

[0087] (1) Figure 1 Ni-TDC prepared in Example 1-3 x BDC 1-x And the X-ray powder diffraction patterns of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Figure 1 It can be seen that when H2BDC is introduced into Ni-TDC, the (020) crystal plane of Ni-TDC at 9.5° gradually shifts to a lower angle (9.0°), indicating that Ni-TDC x BDC 1-x There is lattice expansion in the Ni-TDC. At the same time, with the increase of H2BDC content,x BDC 1-x The crystal plane strength in the Ni-TDC 0.6 BDC 0.4 The crystal plane strength is the weakest, indicating that its ligand competition is the most intense and the tensile strain is the largest.

[0088] Figure 2 Ni-TDC prepared in Example 1-5 x BDC 1-x And the Raman spectra of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Figure 2 It can be seen that Ni-TDC 0.6 BDC 0.4 At 862cm -1 A new peak appeared at , which corresponds to the CH bending vibration of the H2BDC plane, indicating that the H2BDC ligand was successfully introduced. 0.6 BDC 0.4 Carboxylic acid group (COO - ) shows a stretching vibration peak from 1474 cm -1 Redshift to 1460 cm -1 , the red shift of this Raman peak also confirms the generation of lattice strain.

[0089] (2) Figure 3 Ni-TDC prepared in Example 1-3 x BDC 1-x And the scanning electron microscope images of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Among them, a is the Ni-TDC of Comparative Example 1; b is the Ni-TDC of Example 2 0.8 BDC 0.2 ; c is the Ni-TDC of Example 1 0.6 BDC 0.4 ; d is the Ni-TDC of Example 3 0.2 BDC 0.8 ; e is the Ni-BDC of Comparative Example 2. Figure 3 It can be seen that Ni-TDC 0.6 BDC 0.4 It has a two-dimensional nanosheet morphology and is evenly dispersed on the substrate CFP. The flexible nanosheets at the edge will also curl spontaneously when drying. Compared with the three-dimensional stacking structure of Examples 2-3 and Comparative Examples 1-2, Ni-TDC 0.6 BDC 0.4 The unique flaky structure will give it a larger specific surface area, more active sites and faster mass transfer rate.

[0090] (3) Figure 4Ni-TDC prepared in Example 1 0.6 BDC 0.4 Among them, a is a transmission electron microscope image; b is a high-resolution transmission electron microscope image; c is the distribution map of each element; d is an atomic force microscope image. Figure a further confirms that Ni-TDC 0.6 BDC 0.4 Figure b shows that the lattice fringe spacing is 0.94nm, corresponding to Ni-TDC 0.6 BDC 0.4 (020) crystal plane. At the same time, distorted lattice fringe regions were also observed, further confirming that Ni-TDC 0.6 BDC 0.4 There is lattice strain in the Ni-TDC, and these lattice defects may expose more active sites, thereby improving the efficiency of OER. Figure c shows that Ni-TDC 0.6 BDC 0.4 The Ni, C, O and S elements are evenly distributed, indicating that the introduction of H2BDC ligands does not cause heterogeneous coordination between the ligand functional groups and metal ions. Figure d confirms that Ni-TDC 0.6 BDC 0.4 It has an ultra-thin nanosheet morphology with a thickness of only 6nm.

[0091] (4) Figure 5 Ni-TDC prepared in Example 1 0.6 BDC 0.4 And the thermogravimetric curves of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Figure 5 The decomposition of each material is divided into three stages. Ni-TDC 0.6 BDC 0.4 The first weight loss at 0-210 °C corresponds to H2O adv The second weight loss from 210℃ to 285℃ is due to Ni-TDC 0.6 BDC 0.4 Thermal decomposition of the organic framework. The third weight loss from 285°C to 550°C is attributed to Ni-TDC 0.6 BDC 0.4 It is worth noting that Ni-TDC 0.6 BDC 0.4 The thermal decomposition temperature of the organic framework is significantly lower than that of Ni-TDC and Ni-BDC, which indicates that the defect-rich Ni-TDC 0.6 BDC 0.4 There is a defect structure (lack of coordination) between the ligand and the metal.

[0092] (5) Figure 6 Ni-TDC prepared in Example 1 0.6BDC 0.4 And the nitrogen isothermal adsorption-desorption curves of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Figure 6 It can be seen that Ni-TDC 0.6 BDC 0.4 , Ni-TDC and Ni-BDC all show type II isotherms with H3 hysteresis loops. Among them, the pore sizes of Ni-TDC and Ni-BDC are both larger than 20nm, belonging to macroporous structures, while Ni-TDC 0.6 BDC 0.4 The pore size is 7.4nm, which belongs to the mesoporous structure. 0.6 BDC 0.4 The BET surface area is 47.5 m 2 / g, which is much larger than Ni-TDC and Ni-BDC. These results show that the presence of lattice strain and oxygen vacancies significantly changes the coordination structure of Ni atoms and increases the Ni-TDC 0.6 BDC 0.4 Specific surface area.

[0093] (6) Figure 7 Ni-TDC prepared in Example 1 0.6 BDC 0.4 And the X-ray photoelectron spectra of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Among them, a is the high-resolution XPS spectrum of O1s; b is the high-resolution XPS spectrum of Ni 2p. XPS spectrum shows that Ni-TDC 0.6 BDC 0.4 The presence of Ni, C, O, and S elements is consistent with EDX characterization. In Figure a, the characteristic peak at 530.0-530.5eV can be attributed to Ni-O, the characteristic peak at 531.5-532.0eV can be attributed to CO, and the characteristic peak at 531.6eV can be attributed to oxygen vacancies (O v ), the characteristic peak at 533~533.5eV can be attributed to adsorbed water (OH adv ). It is worth noting that compared with Ni-TDC and Ni-BDC, Ni-TDC 0.6 BDC 0.4 The CO bond binding energy shifted, which may be due to the change in the coordination environment of the ligand O caused by the competition for coordination between the two ligands. The Ni-O bond showed a shift toward a lower binding energy, indicating that the two-ligand strategy allowed more electrons to be transferred from Ni to O atoms, thereby enhancing the electron transfer between metal and oxygen. As shown in Figure b, the peaks at 855.8eV and 873.6eV are attributed to the Ni 2p 1 / 2 and Ni 2p 3 / 2, accompanied by two satellite peaks at 861.4eV and 878.9eV (labeled as "Sat."), indicating that Ni is in a divalent state. It is worth noting that compared with Ni-TDC and Ni-BDC, Ni-TDC 0.6 BDC 0.4 The Ni 2p peak shifts to a higher binding energy by 0.14 eV. This can be attributed to the lattice strain caused by the competitive coordination of the ligands, which induces the formation of oxygen vacancies. These lattice strains and the presence of oxygen vacancies affect the electronic structure of Ni atoms, causing the Ni 2p peak to shift to a higher binding energy. Through electronic configuration studies, it was found that for Ni 2+ (t 2g 6 e g 2 ) ions, after losing electrons, their electronic configuration is closer to the ideal g 1 configuration, this change makes e g The orbitals have a stronger overlap with oxygen-containing adsorbates, which can directly promote the electron transfer between the active sites and the adsorbed reaction intermediates, thereby accelerating the kinetic process of OER.

[0094] (7) Figure 8 Ni-TDC prepared in Example 1 0.6 BDC 0.4 And the electron paramagnetic resonance curves and near-edge absorption spectra of Ni-TDC and Ni-BDC prepared in Comparative Examples 1-2. Wherein, a is the electron paramagnetic resonance curve; b is the near-edge absorption spectrum of NiK edge; c is the NiK edge X-ray absorption fine structure spectrum; d is the k 3 Wavelet transform of weighted EXAFS signal; e is a demonstration diagram of lattice distortion and electron spin state. In Figure a, Ni-TDC 0.6 BDC 0.4 The strongest EPR signal characteristic peak was shown, with a g value of 2.003, while the single ligand Ni-TDC and Ni-BDC did not show EPR signals. The EPR signal intensity was positively correlated with the degree of ligand competition, indicating that the dual ligand strategy was successful in Ni-TDC. 0.6 BDC 0.4 The coordination competition is triggered, which leads to the structural strain of MOF and induces the formation of oxygen vacancies. A wealth of localized electrons are formed at the oxygen vacancies, which can effectively affect the electronic state of metal atoms and provide active sites for catalysis. In addition, the oxygen vacancies on the surface can strongly attract active molecules, thereby improving the catalytic activity. As shown in Figure b, Ni-TDC 0.6 BDC 0.4The spectral profiles of Ni-TDC and Ni-BDC nanosheets are close to that of NiO, indicating that the average valence state of Ni is around +2. The edge front peak at 8340 eV reflects the electron transition process from 1s orbital to 3d orbital, where the peak intensity reflects the number of unoccupied orbitals. Specifically, compared with Ni-TDC and Ni-BDC, Ni-TDC 0.6 BDC 0.4 The edge front red shift indicates that the 3d orbital has a stronger affinity for transition electrons, because empty orbitals are more likely to attract transition electrons than half-filled orbitals. Therefore, Ni-TDC and Ni-BDC have more unpaired electrons, while Ni-TDC 0.6 BDC 0.4 There are more empty orbitals in Ni-TDC. 0.6 BDC 0.4 The white line peak shows the characteristics of broadening and weakening, indicating that the lattice strain leads to a decrease in the Ni-O coordination number. As shown in Figure c, at about A characteristic peak appears at , corresponding to Ni-O coordination. It can be observed in Figure d The Ni-O coordination characteristic peak is consistent with the above inference. As can be seen from Figure e, Ni-TDC 0.6 BDC 0.4 The coordination number of Ni in the Ni-TDC (5.6) is smaller than that of Ni-TDC (6.0) and Ni-BDC (6.0), indicating the presence of unsaturated coordination. Interestingly, the unsaturated coordination leads to the 0.6 BDC 0.4 The bond length of Ni-O in Longer than Ni-TDC and Ni-BDC The presence of unsaturated coordination and the change in Ni-O bond length will break the original octahedral symmetry, resulting in structural distortion. In addition, the decrease in the intensity of the Ni-O bond peak in Figure c also confirms the increase in the degree of NiO octahedral distortion. The above results show that before the introduction of defects, there are more unpaired electrons in the Ni 3d orbitals of Ni-TDC and Ni-BDC occupying the e g After the introduction of defects, the octahedral symmetry of NiO is destroyed due to the presence of unsaturated coordination and the increase of Ni-O bond length, which makes Ni 2+ From high spin state to low spin state. Ni-TDC 0.6 BDC 0.4 The unsaturated coordination of low-spin Ni sites in the cations leads to proper hybridization between Ni 3d and O 2p orbitals and results in fast OER kinetics.

[0095] (8) Figure 9 Ni-TDC prepared in Example 10.6 BDC 0.4 A series of in situ Raman spectra. Among them, a is the electrochemical in situ Raman experiment setup (WE is the working electrode; CE is the counter electrode; RE is the reference electrode), bc are Ni-TDC 0.6 BDC 0.4 Three-dimensional projection image and two-dimensional Raman intensity image of electrochemical in situ Raman spectrum in the potential range of 1.0~1.6V (vs.RHE). As shown in Figures bc, when the potential is higher than 1.36V (vs.RHE), the peak at 474cm -1 and 555cm -1 Two new peaks appear at Ⅲ -E of the O key g Bending vibration and A 1g Stretching vibration. As the potential increases, 486cm -1 The peak gradually red-shifted to 474 cm -1 , which shows that Ni Ⅱ -O to Ni Ⅲ -O transformation process. More importantly, 474cm -1 and 555cm -1 The relative intensity of the characteristic peaks at 555 cm reflects the phase transition of NiOOH. -1 The peak intensity at 474 cm -1 The β-NiOOH is stronger in the γ-NiOOH region, indicating that it contains more β-NiOOH. Compared with γ-NiOOH, β-NiOOH has a higher oxidation state and thus exhibits stronger intrinsic OER activity.

[0096] (9) Figure 10 Ni-TDC prepared in Example 1 0.6 BDC 0.4 And the density functional theory calculation diagram of Ni-TDC and Ni-BDC prepared in Comparative Example 1-2. 0.6 BDC 0.4 / NiOOH differential charge density diagram, side view, main view and two-dimensional charge density diagram; d is the four-electron transfer mechanism; e is the state density diagram; f is the Gibbs free energy diagram. As can be seen from Figures ac, there is a large amount of charge accumulation at the interface, which confirms that NiOOH and Ni-TDC 0.6 BDC 0.4 The strong electronic interaction between Ni and O atoms is conducive to faster electron transfer. The stronger charge transfer phenomenon between Ni and O indicates that more electrons are transferred from Ni to O, which is consistent with the XPS results after electrochemistry. This electron transfer from Ni to neighboring O atoms will lead to an increase in high-valent Ni active sites, which is conducive to promoting the deprotonation of the adsorbate. As shown in Figure d, Ni-TDC0.6 BDC 0.4 / NiOOH intermediates. As shown in Figure e, Ni-TDC 0.6 BDC 0.4 The density of states (DOS) of Ni-TDC / NiOOH near the Fermi level is significantly higher than that of Ni-TDC / NiOOH and Ni-BDC / NiOOH, indicating that Ni-TDC 0.6 BDC 0.4 / NiOOH has better conductivity. In addition, Ni-TDC 0.6 BDC 0.4 / NiOOH d-band center (ε d ) is -1.51eV, which is closer to the Fermi level than Ni-TDC / NiOOH (-1.98eV) and Ni-BDC / NiOOH (-1.63eV), indicating that the presence of oxygen vacancies and unsaturated coordination effectively optimizes the electronic structure and d-band center of the Ni site, which is beneficial to the formation of oxygen-containing intermediates in Ni-TDC. 0.6 BDC 0.4 / NiOOH surface adsorption. As shown in Figure f, RDS is the conversion step from OH* to O*, among which Ni-TDC 0.6 BDC 0.4 / NiOOH has a ΔG2 of 1.45eV, which is significantly lower than that of Ni-TDC / NiOOH (2.00eV) and Ni-BDC / NiOOH (1.66eV). 0.6 BDC 0.4 The spin state of the Ni site in / NiOOH effectively optimizes the overlap between Ni 3d and O 2p orbitals, thereby achieving faster deprotonation in the Ni-OH* process and reducing the OER overpotential.

[0097] 2. Electrochemical testing

[0098] Test method: All electrochemical measurements were performed using a multi-channel electrochemical workstation (Bio-logic VMP3, France) with a typical three-electrode system in 1.0 M KOH solution. The prepared catalyst, carbon rod, and Hg / HgO electrode were used as the working electrode, counter electrode, and reference electrode, respectively. The voltage was set at 5 mV s in the range of 1.2–1.8 V (vs. RHE). -1 Linear sweep voltammetry (LSV) was performed at a scan rate of 1.5 Å, and all polarization curves were corrected for iR (95%). The measured potentials were converted to the RHE scale using the Nernst equation:

[0099] E RHE =E SCE +0.241+0.059pH-iR

[0100] Where i is the tested current and R is the solution impedance.

[0101] Test results:

[0102] (1) Figure 11 Ni-TDC prepared in Example 1-3 x BDC 1-x And the electrochemical performance test results of Ni-TDC and Ni-BDC prepared in 1.0M KOH in Comparative Examples 1-2. Among them, a is the linear sweep voltammetry curve; b is the Tafel slope graph; c is 10mA cm -2 The overpotential and Tafel slope of the catalyst at the time of d are compared with those of the catalyst in the prior art; d is the electrochemical impedance spectroscopy; e is the double layer capacitance (C dl ) figure; f is the turnover frequency (TOF) curve; g is the OER mass activity at 300 mV; h is 10 mA cm -2 and 100mA cm -2 Ni-TDC 0.6 BDC 0.4 As shown in Figures ab, Ni-TDC 0.6 BDC 0.4 The oxidation peak corresponds to Ni 2+ Towards high price Ni 3+ / 4+ The conversion of species was observed at lower potentials and the intensity was much greater than that of Ni-TDC and Ni-BDC. 0.6 BDC 0.4 They exhibit excellent electrocatalytic OER activity, requiring only low overpotentials of 230 mV and 316 mV to reach 10 mA cm -2 and 100mA cm -2 The current density is better than that of other control samples and RuO2. The oxidation peak of the polarization curve is attributed to Ni 2+ Towards high valence Ni 3+ / 4+ Species transformation, in which Ni-TDC 0.6 BDC 0.4 The oxidation peak intensity of Ni-TDC is higher and the oxidation potential is lower, indicating that the presence of lattice strain and oxygen vacancies is conducive to exposing more active sites. 0.6 BDC 0.4 Nanosheets (53.3mV dec -1 ) has a significantly lower Tafel slope than Ni-TDC (56.5 mV dec -1 )、Ni-TDC 0.8 BDC 0.2 (78.2mV dec -1 )、Ni-TDC 0.2 BDC0.8 (62.0mV dec -1 ) and Ni-BDC (75.8mV dec -1 ), further proving its fast reaction kinetics. 0.6 BDC 0.4 The overpotential of the nanosheets in alkaline medium (230 mV@10 mA cm -2 ) and Tafel slope (53.3mV dec -1 ) is superior to other previously reported high-performance MOF-based OER catalysts. Figure c is Ni-TDC 0.6 BDC 0.4 Compared with the catalysts reported in the prior art [2D Co-MOF (J. Mater. Chem. A, 2018, 6, 22070-6), Ni-MOF@Fe-MOF (J. Mater. Chem. A, 2018, 6, 22070-6), Co@CNT / NF (Appl. Catal. BEnviron. Energy, 2020, 271, 118939), Co@N-CS / N-HCP@CC (Adv. Energy Mater., 2019, 9, 1803918), Ni-MOF@Fe-MOF (Adv. Funct. Mater., 2018, 28, 1801554), Co / Ni(BDC)2TED (J. Mater. Chem. A, 2019, 7, 18519-28), Fe2V-MOF (ACS Appl.Mater.Interfaces, 2022, 14, 37804-13), IFP-8 (ACS Appl. Energy Mater., 2019, 2, 8930-8), Ni BTC (ChemElectroChem, 2018, 5, 2795-807), S / N-CMF@Fe x Co y Ni 1-x-y -MOF (Adv. Mater., 2023, 35, 2207888), Br-Ni-MOF (A) (Sci. Adv., 7, eabk0919)] overpotential and Tafel slope. As shown in Figure dh, in the fitted Nyquist plot, Ni-TDC 0.6 BDC 0.4 With minimum charge transfer resistance (R ct ) is 0.87Ω, indicating that Ni-TDC 0.6 BDC 0.4 It has a stronger charge transfer ability at the gas-liquid-solid three-phase interface. The cyclic voltammetry (CV) curve is scanned in the non-Faraday region to obtain Cdl , which can indirectly reflect the electrochemically active specific surface area (ECSA) of nanomaterials. 0.6 BDC 0.4 With the largest C dl 2.41mF cm -2 , indicating that it has the largest ECSA, which may expose more active sites and have better catalytic performance. Figure fg shows that at the same potential, Ni-TDC 0.6 BDC 0.4 The TOF value of Ni-TDC exceeds that of other catalysts, indicating that it has excellent OER conversion efficiency and strong intrinsic catalytic activity. 0.6 BDC 0.4 The performance of Ni-TDC is particularly outstanding, further verifying that the coordination defect improves the intrinsic activity of the active site. Figure h shows that Ni-TDC 0.6 BDC 0.4 showed remarkable OER stability at 10 mA cm -2 and 100mA cm -2 After continuous operation for 100 h, the overpotential has no obvious change, indicating its excellent stability.

[0103] (2) Figure 12 The whole water decomposition process and results are shown in Figure 1. 0.6 BDC 0.4 Polarization curves of the two-electrode system composed of the Pt / C electrode material prepared in Comparative Example 3 and the RuO2 electrode material prepared in Comparative Example 4 in 1.0 M KOH, c is the Ni-TDC prepared in Example 1 0.6 BDC 0.4 Comparison of the voltage of the two-electrode system composed of the Pt / C electrode material prepared in Example 3 and the full water splitting cell reported in the prior art, d is the Ni-TDC prepared in Example 1 0.6 BDC 0.4 The stability test results of the two-electrode system composed of the Pt / C electrode material prepared in Example 3. As shown in Figure b, Ni-TDC 0.6 BDC 0.4 (+) ||Pt / C (-) The required battery voltage is only 1.50V and 1.74V to achieve 10mA cm -2 and 100mA cm -2 The current density is better than RuO2 (+) ||Pt / C (-)The performance of the Ni-TDC prepared by the present invention is shown in FIG. 0.6 BDC 0.4 It has excellent full hydrolysis performance. Figure c is Ni-TDC prepared by Example 1 of the present invention 0.6 BDC 0.4 The two-electrode system composed of the Pt / C electrode material prepared in Comparative Example 3 is similar to the full water decomposition battery reported in the prior art [Co-BTC (Chem. Eng. J., 2022, 446, 137045), FeNi(BDC)(DMF, F) / NF (Appl. Catal. B Environ. Energy, 2019, 258, 118023), Fe2V-MOF (ACS Appl. Mater. Interfaces, 2022, 14, 37804-13), Fe-Co-Ni MOF (J. Am. Chem. Soc., 2022, 144, 3411-28), CdFe-BDC (ACS Appl.Mater.Interfaces,2022,14,46374-85)、Fe-ZIF-67NFs(Inorg.Chem.,2021,60,4034-46)、Ru@CoFe / D-MOFs(Inorg.Chem.Front.,2022,9,6158-66)、Co(OH)2@NCNT@NF(Nano Energy,2018,47,96-104)】Comparison of voltage. As shown in Figure d, Ni-TDC 0.6 BDC 0.4 (+) ||Pt / C (-) At 100mA cm -2 The potential showed no obvious decay after continuous operation for 100 h at a constant current density of 1.5 wt %.

[0104] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing defect-rich dual-ligand metal-organic framework ultrathin nanosheets, characterized in that: dissolving a nickel source, 1,4-terephthalic acid, and 2,5-thiophenedicarboxylic acid in an organic solvent to obtain a reaction solution; placing a carrier in the reaction solution to perform a solvothermal reaction to obtain the defect-rich biligand metal organic framework ultrathin nanosheet; The dual ligands are 1,4-terephthalic acid and 2,5-thiophenedicarboxylic acid; The ratio of the sum of the amount of nickel atoms in the nickel source and the amount of the double ligand is 1:1; in terms of molar ratio, the nickel atoms in the nickel source: 1,4-terephthalic acid = 1: (0.2-0.8).

2. The method for preparing defect-rich biligand metal organic framework ultrathin nanosheets according to claim 1, wherein: The nickel source is nickel nitrate hexahydrate; the organic solvent is N,N-dimethylformamide aqueous solution; and the carrier is carbon fiber paper.

3. The method for preparing defect-rich dual-ligand metal organic framework ultrathin nanosheets according to claim 1, characterized in that: The usage ratio of the nickel source to the organic solvent is 0.5 mmol:6 mL.

4. The method for preparing defect-rich biligand metal organic framework ultrathin nanosheets according to claim 2, wherein: The volume ratio of N,N-dimethylformamide to water in the N,N-dimethylformamide aqueous solution is 4:

2.

5. The method for preparing defect-rich biligand metal organic framework ultrathin nanosheets according to claim 1, wherein: The temperature of the solvent thermal reaction is 120° C., and the time of the solvent thermal reaction is 12 h.

6. The method for preparing defect-rich dual-ligand metal organic framework ultrathin nanosheets according to claim 1, wherein: The method also includes pretreatment of the carrier, specifically: first cutting the carbon fiber paper into 1cm×2cm size, then performing a hydrothermal reaction in a dilute nitric acid solution, and then washing with deionized water and ethanol respectively.

7. The defect-rich biligand metal-organic framework ultrathin nanosheet according to claim 6, characterized in that: The temperature of the hydrothermal reaction is 100° C., and the time of the hydrothermal reaction is 4 hours.

8. A defect-rich dual-ligand metal-organic framework ultrathin nanosheet prepared by the method for preparing defect-rich dual-ligand metal-organic framework ultrathin nanosheet according to any one of claims 1 to 7.

9. Use of the defect-rich biligand metal-organic framework ultrathin nanosheet as claimed in claim 8 in electrocatalytic oxygen evolution reaction.

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